1. Field of the Invention
The present invention is related to the removal of various organic coatings, polymerized photoresists, and especially implant and deep-UV hardened photoresist layers during the manufacture of semiconductor or ceramic devices.
2. Description of the Related Art
Stripping of the photoresists and other organic polymers is one of the necessary steps in the manufacturing of semiconductor devices. The stripping of photoresists and organic masks is usually carried out by one of two methods, commonly known as dry and wet stripping or etching. Wet stripping of photoresists, typically involves the use of specialized oxidizing solutions such as Caro's acid and other organic strippers. Dry stripping methods, on the other hand, remove photoresists by oxygen plasma (ashing), and in some cases, with the assistance of hydrogen plasma. However, as semiconductor device geometries increasingly move into submicrometer range, neither dry nor wet stripping techniques seem to provide a satisfactory solution to the problem of complete removal of the photoresists, without damaging the device. Often, a combination of both methods or even consecutive steps of dry plasma etching must be used to achieve this goal.
The major problem with the wet stripping methods arises from the surface hardening of the photoresists due to reactive ion etching (RIE) or ion implantation processes. Similarly, post bakes and UV cures may cause chemical changes in the photoresists that would cause the removal of the resists to be incomplete by conventional wet strippers. Dry plasma etching, using oxygen (ashing), provides an attractive alternative in such cases. However, ashing techniques have also proved, in many instances, to suffer from similar limitations as wet stripping methods. For example, in the case of high-dose ion-implanted resist layers, impurities in the resist may give rise to ash-resistant oxides, which must then be removed by hydrogen plasma followed by ashing and downstream stripping.
Other problems associated with plasma etching and ashing include radiation damage and residual contaminations. Sidewall polymer formations can also occur as a result of the interaction of the released by-products of the plasma etching with the sidewalls of the resist structure. Such polymers cannot be easily removed by simple ashing techniques. A major problem arises from metal impurities typically found in the commercial photoresists. Ashing not only is ineffective in removing trace metal contaminants, it may cause the metal impurities to be driven into the silicon substrates by the high-energy plasma. Wet strips are, in principle, more efficient in removing metal impurities. However, wet strips leave behind the metallic impurities, indigenous to solvents themselves, along with trace organic residues resulting from resist build-up in the solution. They are also not very effective in removing chemically altered resists.
Both methods suffer from severe limitations when organic materials are present in submicrometer grooves and narrow crevices. Both grooves and crevices render the wet strip solutions ineffective by limiting the solvent access, due to surface tension and capillary actions, to the organics. Dry ashing often fails to completely remove photoresists from crevices due to micromasking of the resists by the sputtered oxide (e.g., in planarization processes). On the other hand, in the case of submicrometer grooves, removal of the polymers formed on the side-walls becomes ineffective due to the composition of these polymers. Post etch clean-ups involving removal of the polymeric side wall coating from submicrometer grooves also suffer similar handicaps.
Oxide etch processes also leave carbon-fluorine polymers which are often difficult to remove by dry or wet methods. Even successive application of dry and wet strip followed by RCA clean (a process developed by RCA which involves treatment by NH.sub.4 OH/H.sub.2 O.sub.2 followed by HCl/H.sub.2 O.sub.2) is not very effective in removing such polymers. Finally, both wet and dry stripping techniques present problems in removal of the photoresists used in deep-UV lithographic techniques.
At the present time, a satisfactory method of one-step-removal of photoresists and polymer films, without trace metal contamination problems, and applicable to submicrometer grooves and crevices is not available. The ability to provide a simple method of resist stripping, without the limitations of the conventional wet and dry strippers, should prove very beneficial in improving the architecture, efficiency, throughput, and the performance of the semiconductor devices and related technologies.